20个 Java 优秀实践，让你的代码更丝滑

Long idNumber;
long idNumber; // long 比 Long 占用更少的内存

int birthYear;
short birthYear; // 更好，因为出生年份不能超过 32767 

int personRunningSpeedKmHour;
byte personRunningSpeedKmHour; // 更好，因为一个人的速度不能超过 127 公里/小时

public boolean isOdd(int num) {
return (num & 1) != 0;
} 
// 判断数字为奇数的最佳方法

String name = null; // 冗余
int speed = 0; // 冗余
boolean isOpen = false; // 冗余


String name; 
int speed;
boolean isOpen;
// 这样更清晰

public int age; // 非常差
int age; // 差
private int age; // 好

String s1 = new String("AnyString") ; // 不好：初始化慢
// 需要构造函数创建一个新对象，并将文字添加到堆中


String s2 = "AnyString" ; // 好：快速实例化
// 此快捷方式引用字符串池中的项
// 并且仅当文字不在字符串池中时才创建新对象。

String address = streetNumber +" "+ streetName +" "
+cityName+" "+cityNumber+" "+ countryName; // 差


StringBuilder address = new StringBuilder(streetNumber).append(" ")
.append(streetName).append(" ").append(cityName).append(" ")
.append(cityNumber).append(" ").append(countryName); // 好

int myMoneyInBank = 58356823;
int myMoneyInBank = 58_356_823; // 更易读

long billsToPay = 1000000000L;
long billsToPay = 1_000_000_000L; // 更易读

for (int i = 0; i < names.length; i++) {
  saveInDb(names[i]);
}


for (String name : names) { 
  saveInDb(name);
} // 更清晰

Scanner scanner = null;
try {
  scanner = new Scanner(new File("test.txt"));
  while (scanner.hasNext()) {
    System.out.println(scanner.nextLine());
  }
} 
catch (FileNotFoundException e) {
  e.printStackTrace();
} 
finally {
  if (scanner != null) {
    scanner.close();
  }
}
// 容易出错，因为我们可能会忘记在 finally 块中关闭扫描器



try (Scanner scanner = new Scanner(new File("test.txt"))) {
  while (scanner.hasNext()) {
    System.out.println(scanner.nextLine());
  }
} 
catch (FileNotFoundException fnfe) {
  fnfe.printStackTrace();
} 
// 更清晰更简洁

try { 
  productPrice = Integer.parseInt(integer); 
} 
catch (NumberFormatException ex){
} 
// 静默失败，不提供任何反馈


try {
  productPrice = Integer.parseInt(integer);
} 
catch (NumberFormatException ex) {
  unreadablePrices.add(productPrice); // 处理错误
  log.error("Cannot read price : ", productPrice );// 打印正确且有意义的消息
}

// 先决条件：person 类重写 equals() 和 hashCode() 
Person  p1  =  new  Person ( "John" , "Doe" ); 
Person  p2  =  new  Person ( "John" , "Doe" ); 

System.out.println(p1 == p2); // false
System.out.println(p1.equals(p2)); // true

public final class Person {
    private final String name;
    private final long idNumber;

    public Person(String name, long idNumber) {
        this.name = name;
        this.idNumber = idNumber;
    }

    public boolean equals(Object other) {
        if (other == this) return true;
        if (other == null) return false;
        if (other.getClass() != this.getClass()) return false;
        Person that = (Person) other;
        return (this.name.equals(that.name)) && (this.idNumber == that.idNumber);
    }

    public String toString() {
        return name + " " + idNumber;
    }

    public int hashCode() {
        return Objects.hash(idNumber, name);
    }
}



// 这个类可以转化为一条记录：
record Person(String name, long idNumber) { } // 更简洁

public final class MyValues {
  private MyValues() {
    // 无需实例化类，我们可以隐藏其构造函数
  }
  public static final String VALUE1 = "foo";
  public static final String VALUE2 = "bar";
}

// <-- 空行
@Repository 
public class ...